Exemplary embodiments of the present invention relate to semiconductor device fabrication technology, and more particularly, to a switching device for providing a bipolar (or bidirectional) current path and a memory device having the same.
In general, a unit cell of a semiconductor memory device has a 1S-1M structure that is a combination of a switching part and a memory part which stores data. For example, a resistive random access memory (ReRAM) device esteemed as the next-generation memory device includes a switching part using transistors or diodes and a memory part using a variable-resistance material such as a transition metal oxide.
Meanwhile, a semiconductor memory device uses a bipolar switching method in order to secure the desired characteristics with respect to an operating voltage, a leakage current, an operating speed, and durability. For example, a resistive memory device uses voltages of opposite polarities for a bipolar switching. According to the voltages of opposite polarities, a set operation where a memory part is changed from a high-resistance state to a low-resistance state is performed, and a reset operation where a memory part is changed from a low-resistance state to a high-resistance state is performed. In order to implement a bipolar switching mode of a semiconductor memory device, a switching part is to be configured to provide a bipolar current path.
In the conventional art, a diode is used as a switching part to provide a unipolar (or unidirectional) current path. The diode has a very low reverse current, thus making it difficult to implement stable bipolar switching characteristics. Also, a transistor may be used as a switching part to provide a bipolar current path. However, as the integration density of semiconductor memory devices increases, the size of a transistor which is difficult to be reduced may become a burden in a circuit design. A reduction in the transistor size may degrade the operational characteristics.